Slitters which slit a long web, such as a paper or a cloth, in a transporting direction of the web to provide a predetermined width of a web have been used in various fields. To change a width of a web to be slit, it is necessary to provide a slitter moving mechanism, in which several slitters are arranged at intervals corresponding to several widths. One or more upper blades are moved to slitting positions for serving as slitters whereas they are retracted to retracted positions to stop the function of slitters when not used.
FIGS. 5 and 6 are diagrammatic front and side views showing a substantial structure of a conventional slitter moving mechanism according to the prior art. The slitter includes an upper blade unit 42, having an upper blade 42a, and a lower blade unit 43 having a lower blade 43a. The upper blade 42a and lower blade 43a are brought into contact with each other to rotate in a web transporting direction (arrows X, Y in FIG. 6) at positions where the upper and lower blades 42a and 43a come into contact with the web 41, so that the web 41 which passes between the upper and lower blades 42a and 43a is slit.
The upper blade 42a is provided so that it is movable beween a slitting position, indicated by the solid line in FIG. 5, and a retracted position shown by the dot-and-dash line where the web 41 is prevented from passing through there. A supporting member 42b on which the upper blade 42a is mounted is spring-biased by a coil spring 42c so as to withdraw the upper blade 42a to the retracted position and the upper blade 42a is moved to the slitting position so as to abut with the lower blade 43a by energizing a solenoid 42d.
In the conventional slitter moving mechanism, the displacement d2 of the upper blade 42a becomes excessively large (15 mm, for example) since as shown in FIG. 5 the upper blade 42a is diagonally moved. This can cause the transmission element 42e, such as a chain or a belt, which rotates the upper blade 42a becomes twisted and exerts a lateral force on the transmission element 42e, causing the latter to move out of the transmission sprocket wheel or pulley.
To avoid such an accident of the transmission element 42e the upper blade 42a might be lifted vertically and upwardly from the slitting portion. However, when the upper blade 42a is moved only in a vertical direction, it happens that the upper blade 42a rides over the lower blade 43a without making side-by-side contact therebetween due to machining errors, attachment errors, plays thereof, etc. of the upper blade 42a or lower blade 43a.
To eliminate the above described problems of overriding of the upper blade and moving of the transmission element out of the pulley, the upper blade 42a may be slightly moved in the lateral direction of the arrow Z in FIG. 5 from the slitting position, to be disengaged from the lower blade 43a, and then the upper blade 42a may be elevated in the arrow direction W and moved to the retracted position. When the upper blade 42a is to move from the retracted position to the slitting position, the upper blade 42a is operated in the reverse sequence By moving the upper blade 42a in this fashion with slight lateral displacement of the upper blade 42a, for example, about 0.5 mm enables the transmission element 42e is prevented from being displaced from the sprocket wheel or the pulley This also prevents the overriding of the upper 42a. Such lateral and vertical movements of the upper blade 42a make the slitter moving mechanism more complicated thus causing a considerable rise in failure rate and equipment cost of the slitter moving mechanism.